Gas discharge tube and circuit therefor



March 24, 193 C W, ELL 2,034,756

GAS DISCHARGE'TUBE AND CIRCUIT THEREFOR Filed Nov. 29, 1933 2 Sheets-Sheet 1 MAW [[[67'3005 INVENTOR c.w. HANS ELL BY m ATTORNEY March 24, 1936. Q w HANSELL 2,034,756

GAS DISCHARGE TUBE AND CIRCUIT THEREFOR Filed Nov. 29, 1933 2 Sheets-Sheet 2 3' rg L 7 I 5mm! E 5- r 1 00/707 i E i 22 T:-

w Al 5mm 4400014750 age/0 wear RE INPUT C.W. HANSELL ATTORNEY Patented Mar. 24, 1936 GAS DISCHARGE TUBE AND CIRCUIT THEREFOR Clarence W. Hansell, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application November 29, 1933, Serial No. 700,250

7 Claims. (01. 179-471) This invention relates to a novel gas discharge device and to a novel circuit in which the gas discharge tube may be included to operate as a signal rectifier and/or amplifier.

Heretofore, gas discharge tubes, such as those containing neon, mercury, vapor, or other gases, have been considered unsuitable for use as amplifiers because it has been thought that they have either practically open circuit resistance or very low resistance, depending upon whether or not the gas has been broken down by an electrical discharge. In other words, they are expected to exhibit all the properties of a dielectric or insulator until they begin to ionize, after which point of operation they become conductive to such an extent as to almost present a short circuit.

Obviously, gas discharge tubes as known heretofore are unsuitable in operation in any circuit where proportional amplification, detection or power relaying is desired. This is due to the fact that, as indicated above, as soon as the voltages applied reach a predetermined point the gas in the tube becomes ionized and any increase in applied potential results in considerable ionization taking place and results in a short circuit through the gas of the tube.

Applicant has found that if certain conditions are satisfied a gas discharge tube can be made to operate very much like a three electrode tube. Applicant has also found that by the use of such a tube considerable voltage and power amplification can be obtained. Applicant has further found that a tube of the cold electrode gas discharge type, constructed in accordance with the present invention, will handle high voltages and/or powers where the waves to be detected or amplified are ultra short and the sensitiveness of response of the tube may be considerably increased by placing the tube in a magnetic field of proper strength.-

Briefly, applicants novel discharge tube comprises a thermionic envelope filled with gas at low pressure. The envelope includes four electrodes, the two main electrodes of which are of relatively large area and large spacing and the control electrodes of which are small and so shaped and spaced as to cause a relatively high potential gradient to be maintained in the space between them for relatively low potential differences. By using this structure the control electrodes in effect form a needle gap in which relatively low voltages can produce sufficient potential gradient in the gap to cause ionization.

If a high direct current potential is applied between the spaced electrodes to cause the gas to ionize so that said tube approaches but never reaches a point at which an arc discharge takes place, and smaller potentials are applied to the relatively close electrodes, we have a gaseous discharge amplifier and/or detector because small changes in the potential applied to the closely spaced electrodes will cause changes in the current fiow or ionization of the gas between the widely spaced highly charged electrodes. These changes in current can produce much larger changes in potential between the large widely spaced electrodes than were applied to the control electrodes. Now by utilizing proper potentials and/or by including high resistances in the widely spaced electrode circuit, the tendency for the device to form an unstable arc discharge can be obviated. A large amount of amplification may be obtained with stable operation. Obviously if alternating currents are superposed on the direct current applied between the closely spaced electrodes they will produce ionization of the gap between the large electrodes which are highly charged and consequently produce corresponding amplified currents and potentials in the circuit connected with said large electrodes.

When the tube is passing the small ionization current between the two main electrodes we may vary the number of free ions and electrons in the tube by applying a voltage across the two needle electrodes. This produces additional ions and electrons in and around the needle gap, considerable portions of which are drawn towards the two main electrodes and constitute a flow of current in the main electrode circuit. The great difference in shape, size and spacing of the main electrodes and control electrodes requires that much higher voltages be applied to the main electrodes than to the control electrodes to produce ionization and to produce a flow of current. Consequently, the tube is capable of producing amplification.

The sensitivity of the tube may be considerably increased, particularly when the gas pressure is relatively low, by superimposing a strong magnetic field at right angles to the general directions in which the electrons and ions tend to be moved by the electric fields. The magnetic field tends to bend the paths of electrons and ions and makes the paths longer. As a result any given electric field strength can cause much greater ionization because the magnetic field has greatly increased the probability of secondary ionization of molecules by collisions with ions and electrons.

In all of the above explanation it has been assumed that the values of current used are kept so low that no arc discharge takes place. Under this condition each electron and each ion must batter its way through the gas molecules in the space inside the tube and consequently requires considerable voltage to pull it through. If the are discharge, which is commonly used in gas discharge tubes, could take place, the molecules would be pushed away from the arc path and the are resistance would be very low. Consequently, if the arc condition were permitted no proportional amplification could be obtained and the tube could be used only in a way similar to the thyratron and grid glow tubes already commercialized in which the control electrodes serve only to start an are but are incapable of extinguishing the arc and stopping the current after it is once started.

A gas discharge tube, if constructed in accordance with my invention and operated in accordance with my invention, will produce considerable amplification and is capable of detecting currents of any frequency. Moreover, such a tube may be utilized in accordance with my present invention to demodulate signal modulated oscillations or to modulate carrier oscillations at signal frequency.

The novel features of the invention have been pointed out with particularity in the claims appended hereto.

The nature of the novel discharge tube and the operation thereof, and the nature and operation of the circuit in which said discharge tube may be used, will be better understood by the detailed description thereof which follows, and therefrom when read in connection with the drawings, throughout which like reference characters indicate like parts, and in which:

Figure 1 shows a discharge tube constructed in accordance with the present invention;

Figure 2 shows the discharge tube of Figure 1 incorporated in an amplification circuit; while,

Figures 3, 3a, 4 and 5 show various circuit arrangements for amplifying and rectifying and multiplying alternating current potentials.

Referring to Figure 1 of the drawings, I indicates the tube closure member which may be of any suitable substance and is preferably of glass. 3 and 5 indicate the main electrodes which, as shown, are of considerable size. The electrode 3 may, for purposes of illustration, be considered the anode, while the electrode 5 may, for purposes of illustration, be considered the cathode. The main electrodes are, as shown, spaced a considerable distance apart in order to increase the discharge resistance between them. 1 and 9 denote a pair of auxiliary electrodes which, for purposes of illustration, will be termed control electrodes. The electrodes are, as indicated, relatively small in size as compared with the main electrodes. The tips of these electrodes are reduced in size and are spaced close together in the path between the main electrodes. The purpose of so arranging and spacing the control electrodes is to insure a relatively high potential gradient in the space near and between them. These control electrodes, as shown, form a needle gap in which relatively low voltages can produce sufiicient potential gradient in the gap to produce ionization of the gas in the tube.

The control electrodes are, as indicated by their name, utilized to control the flow of current between the main electrodes. The weak potentials to be amplified or detected are applied to the control electrodes and the main output circuits are connected between the main electrodes, as has been shown in Figure 2.

In Figure 2 it is assumed that signal modulated oscillations received from any source are to be detected and amplified. These oscillations are impressed on the auxiliary control electrodes 7 and 9. The main electrodes 3 and 5 are connected as shown by way of a resistance R in series with a potential source it. The potential source H) is made relatively high and is preferably made of such a value as to barely start ionization of the gas between the main electrodes. The control electrodes have a lower potential between them but of suficient value to start ionization and permit a flow of current between the main electrodes, the value of which is controlled by the potential or current applied to the control electrodes. The current fiow and the amount of gas ionization is held to a low value under all conditions by means of the resistance R, which may be of a large value. The weak currents applied to the control electrodes 1 and 9 are detected and/or amplified and their modulations appear on the main electrodes 3 and 5 and at the terminals of the resistance R. The amplified modulations may be impressed on the control grid l2 of an additional thermionic amplifier I l connected as shown. The thermionic tube l draws its anode current from the source IE! and also serves the purpose of varying the voltage drop in R to assist in maintaining a low gas discharge current between the main electrodes of the gas discharge tube I, as well as serving to provide a suitable output coupiing. The amplified modulations may be utilized from the secondary winding of a transformer T connected as shown, with the anode of tube [4. By utilizing the tube [4 as shown a large power output may be obtained.

As will appear more in detail hereinafter, the ionization potential between a pair of electrodes is dependent upon the size and spacing of the electrodes. Large and widely spaced electrodes require relatively high potentials between them to produce and maintain a self initiating discharge. Conversely small and closely spaced electrodes require relatively low potentials to produce and maintain a discharge. If a pair of relatively small electrodes as shown in Figures 1 and 2, closely spaced, are in the same vessel as a pair oflarge electrodes, widely spaced, we obtain a gaseous discharge amplifier and detector. Ionization may be initiated and controlled by the relatively low voltages applied to the closely spaced electrodes and the strength of ionization between these electrodes will control the strength of current through the relatively large and widely spaced electrodes through which high voltage and power is applied. Any variations in D. C. or A. C. currents and potentials applied to the electrodes 7 and 9 of the tube I will cause variations in the current between the main electrodes in said tube which appear in the output circuit connected with the electrodes 3 and 5 and in the output of the transformer T.

For demodulation the output circuit should be mainly responsive to the modulation frequencies present in the modulated input energy. For example, the output circuit of the tube I of Figure 2 should respond mainly to the frequency of the signal impressed on the carrier applied to the control electrodes of the tube.

For frequency multiplication and/or amplification by even harmonic ratios it is necessary to make the output circuit responsive to even harmonies of the input frequency.

The gaseous discharge tube; of the present in-.-; vention maybe utilized as an amplifier and, when so utilized,,may beconnected in circuit as in:

dicated in Figure 3. Here the electrodesland- 9 are connected together by. way of. resistances and inductances l and I1 and asource of potential 20 as shown. The inductances l and 11 may be coupled as shown to an input inductance, which may be energized bythe oscillations to,.be am;- plified. This circuit is preferably tuned to the frequency of theoscillationsto be amplified. The oscillations in the circuit connected with the electrodes l and 9 may be shunted around the source 20 and the resistances in series with it by a capacity C as shown.

The main electrodes 3 and 5 are connected together as shown by way of high resistances and inductances with a source of potential 22. The inductances in this circuit may be coupled to an inductance which supplies the amplified oscillations to the utilization circuit. The output circuit or utilization circuit is preferably tuned to the frequency of the oscillations amplified. If the oscillations amplified are of low frequency the transformers may be of the iron core type and untuned as shown in Figure 3.

Where radio frequencies are amplified the input and output circuits are preferably tuned by variable capacities, as shown in Figure 3a.

The resistances shown in the several portions of the input and output circuits serve to limit the maximum obtainable current flow and to balance out any tendency for unstability of oscillations to develop.

By suitable adjustment of the potentials applied to the control electrodes and main electrodes the circuit of Figure 5 may be utilized for demodulating signal carrying oscillations. In this case the input circuits are tuned to the frequency of the carrier while the output circuit is tuned or responsive only to the frequency of the modulations on the carrier.

For demodulating relatively strong signal modulated carrier oscillations some of the resistances may be omitted from the circuits as shown in Figure 4. Here the source of potential connected with the control electrodes 1 and 9 is omitted and the signal carrying oscillations to be demodulated are utilized to cause variations in ionization and current fiow between the output electrodes 3 and 5. The input circuit is tuned as shown by a variable capacity to the carrier frequency oscillations. The output circuit resistance to limit current fiow is provided by the primary windings of the audio frequency transformer T1 connected as shown. The secondary winding of this transformer may be connected with any utilization circuit.

For frequency multiplication the input circuit may be connected as shown in Figure 5, which is in this respect similar to the input circuit of Figure 4. The output circuit, however, includes the current limiting resistances connected as shown and also inductances coupled to an output circuit tuned by a capacity to an even harmonic of the fundamental frequency f. This frequency may be 2 or any even harmonic of the fundamental frequency 1.

Having thus described my invention and the operation thereof, what I claim is:

1. A gas discharge tube including, an envelope filled with gas, a cold electrode in said envelope, an anode in said envelope spaced from said cold electrode, and a pair of small electrodes interposed between said cold electrodes, said small electrodes having tapered ends which are spaced apart from each other to fo'rm a gap in which relatively low potentials applied between said last named electrodes producea high potential gradient.

1 2. A gas discharge tube including, an envelope filled with gas, a cold electrode of relatively large area in said envelope, an anode of relatively large area in said envelope spaced a considerable distance from said cold electrode whereby a large potential is required to produce ionization between said electrodes, and a pair of small electrodes interposed between said large electrodes, said small electrodes being shaped and spaced to form a needle gap in which relatively low applied potentials can produce a high potential gradient in the path between said first named electrodes.

3. Means for relaying oscillating potentials comprising, a gas discharge tube having a gas enclosing envelope, an anode, a cold electrode, and a pair of control elements enclosed in said envelope, said control elements having tapered ends to provide a needle gap in the path between said anode and cold electrode, means for applying oscillating potentials to said control elements, and a source of power and a utilization circuit connected between said anode and col-d electrode.

4. Means for relaying oscillating potentials comprising, a gas discharge tube having a gas enclosing envelope, an anode, a cold electrode, said elements being of relatively large area, and a pair of control elements enclosed in said envelope, said control elements being relatively small and closely spaced to provide a needle gap between said anode and cold electrode, means for applying oscillating potentials to said control elements, and a source of power, a resistance and a utilization circuit connected between said anode and cold electrode.

5. An electrical relay device for converting extremely weak current into current of considerable intensity comprising, a gaseous discharge tube, a pair of comparatively large, widely spaced main electrodes, a pair of comparatively small, closely spaced auxiliary electrodes in the path between said main electrodes, said main electrodes being connected to a source of controlled energy supply of a value sufiicient to produce ionization but not sufiicient to start a discharge, a circuit for applying direct current potentials to said auxiliary electrodes to produce ionization therebetween, and means for superimposing said weak current upon said direct current applied to said auxiliary electrodes, said potential applied to said auxiliary electrode being of such value that upon the superimposing of said weak current the tube becomes ionized so that current flows between said main electrodes.

6. An electrical relay device for producing char-' acteristic current of considerable intensity from extremely weak current comprising, a gaseous discharge tube, a pair of comparatively large, widely spaced main electrodes, a pair of comparatively small closely spaced auxiliary electrodes in the path of said main electrodes, said main electrodes being connected to a source of controlled energy supply of a value sufiicient to produce ionization but not sufficient to start a discharge, a circuit for applying direct current potentials to said auxiliary electrodes to produce ionization therebetween, means for superimposing said weak current upon said direct current applied to said auxiliary electrodes, said potential applied to said auxiliary electrode being of such value that upon the superimposing of said weak current the tube becomes ionized so that current flows between said main produce a discharge between said electrodes, a circuit for superimposing alternating currents to be amplified upon a weak direct current potential and applying the same between said auxiliary electrodesto start ionization in the gap between said main electrodes, current limiting devices connected in circuit with said main electrodes, and a circuit for utilizing the amplified potentials appearing on said main electrodes.

CLARENCE W. HANSEIL. 

